3. Field of the Invention
The invention is directed to a switching matrix network for digital audio signals that are supplied to the inputs of the switching matrix network in parallel representation via incoming data busses in individual sampling clock sequences having sampling frequencies that deviate from one another and are transmitted in identical parallel representation to identical, outgoing data busses via arbitrarily switchable outputs of the switching matrix network, whereby a suitable switching matrix network sampling clock is provided for the switching events within the switching matrix network.
2. Description of the Related Art
It can occur in switching equipment for digitized audio signals in the sound recording studio field that the PCM signals at the inputs of the switching matrix network have different sampling rates. This particularly leads to problems when the couplers had a fixed sampling rate prescribed for them. In systems having a great number of channels, it seems beneficial to use the same coupler for all channels, since, thus, the hardware outlay for the actual switching matrix network can be kept low in comparison to a plurality of sub-couplers having differing "switching rates". The object thus arises to exactly maintain the sampling rate when coupling pulse-code-modulated signals, i.e. that the individual sampling frequency with which a signal is supplied to the input of the switching matrix network should also be preserved in the signal taken from the respectively coupled output. If, namely, the sampling rates were to vary within shorter time intervals, then this would involve a deterioration of the quality of the signal reconstructed after the digital-to-analog conversion.
U.S. Pat. No. 3,868,481 discloses a time-division multiplex through-connect system (switching matrix network) for digital signals that works with different bit rates that derive due to different word lengths (6 or 8 bits per byte) and different combinations of channels (or words) of 6, 12 or 24 channels per frame. In this system, however, the sampling rate for all channels is the same, this, of course, being a prerequisite for these channels to be capable of being combined to form a higher-ranking channel (highway). The incoming signals are converted by input units to a uniform byte and frame format that is then offered to the switching matrix network.
The sampling rate of the outgoing signals is synchronous with the coupler clock multiplied by a rational factor. This must be appropriately selected in order to be able to switch the total of signals sampled with, for example, 8 kHz. A periodic data loss that is compensated by resetting buffer memories (elastic buffers) arises due to slight frequency differences. The system disclosed by the U.S. Patent is not suitable for signals having input sampling frequencies that deviate greatly from one another, as is possible in the switching matrix network of the invention.